Graphshard70 minFrontend Engineer

Notifications Dependency DAG Recovery

Frontend Engineer signal: topological sort + cycle detection in a in-app notification tray context. This is a ProdMatch-owned frontend engineer drill, framed as a April 2026 PhonePe Engagement UX simulation, not a copied platform question.

Company context

PhonePe · Engagement UX

Freshness

April 2026

Product surface

in-app notification tray

ProdMatch interview simulation based on product-team patterns; not a claim of a real company question.

Question

You own in-app notification tray for a Frontend Engineer loop. Given notifications and directed dependencies between them, return a valid execution order. If a cycle exists, return an empty list and identify that the rollout is blocked.

Input

n nodes labelled 0..n-1 and dependency pairs [before, after].

Output

A valid order of all nodes, or [] when dependencies contain a cycle.

Constraints

1 <= n <= 200000
0 <= dependencies.length <= 400000
The graph may be disconnected.

Concepts

render scheduling
state graphs
virtualization
topological sort
cycle detection
dependency graph

notifications: 4, deps: [[0,1],[0,2],[2,3]] -> [0,1,2,3] or [0,2,1,3]

Approach

Try framing your own approach first. The 30 seconds you think before peeking is where learning happens.

Clean Solution

Reveal the approach first.

How well did you understand?

Your rating tunes when this problem shows up again.

Common Mistakes

Mark visited when enqueueing, not after repeated dequeue.
Do not ignore disconnected components if the product surface can have them.

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